1) It has a Control Stick that could be used to navigate in CHDK's or camera's menus. No more wearing to the camera's fragile jog-dial...

2) It has two buttons (called C and Z), that could be used for shutting, and for focus or zoom (one of the two buttons would be the + or increase, and the other one the - or decrease). Two buttons, two different press-time lengths (long, short) = 4 functions.

3) It has an three-axis acelerometer. Now nothing comes to my mind about which CHDK or native camera function could take benefit from it, but I'm sure that you guys will find something

4) It fits nicely in the hand. It's light, and it's available in a lot of colours. This last thing could seem a silly thing, but I'm sure that there will be a lot of people that will be happy to have a controller that is the same colour of their camera.

5) Everything with an I2C can use it. The Arduino community uses it almost for everything, and that means that a lot of intermediate interfaces and code are already available. Just give it a check in your favourite online electronics store or DIY forum.

6) It's really cheap! And can be found even cheaper, if you buy it second-hand. No need to buy it original from Nintendo, there's also third parties' providers. Some of the latter are wireless!

7) I can totally see someone holding and pointing the camera with his left hand, and using the nunchuk with his right hand. Ergonomy is a must!